Embedded audio systems such as those used for mobile phones typically support headsets that include both stereo headphones and mono microphones. Connectivity with these external components is established using 4-terminal 2.5 mm or 3.5 mm jacks on the audio system to which the headset connects. The first two terminals are the standard stereo connections of the headphone. The last two terminals are used for the microphone signals and the headset ground. However, vendors vary by the order of these last 2 terminals. Some vendors follow a standard of the Open Mobile Terminal Platform (OMTP), and others follow the opposite order. On most embedded audio systems this is not an issue, as vendors design headsets compatible for their own systems. But many audio systems are generic (e.g personal computers), and require support for both standards.